With the development of power grids, the maximum short-circuit currents of the power grids in many regions have exceeded the interrupting capacity (63 kA at most, currently) of a breaker. For the sake of this limitation, a more effective short-circuit current breaking technology is desired.
A high-capacity fast switch has been domestically developed early which adopts the combination of an exploding fast breaking current-carrying bridge with a high-voltage current limiting fuse and a zinc oxide resistor having a high energy absorption capacity and which can be switched on/off at the beginning of the rise of a short-circuit current to limit the rise of the short-circuit current and cut off the short-circuit current within 1 ms when the short-circuit current is approximate to 15% of a peak value to avoid the impact caused by a large short-circuit current on an electric device, Although featured by a large rated current (6 kA), a short breaking time (below 3 ms), a high breaking capacity (160 kA) and a high voltage resistance (36 kV) of break, the high-capacity fast switch has defects in use, the removal of a faulted line after switching off the high-capacity fast switch causes potential safety hazards to the stable running of some loads which cannot be powered off, besides, the high-capacity fast switch can only be installed indoor. At present, all the domestic solutions to the loss and the voltage reduction caused during the running of a current limiting reactor are connecting a high-capacity fast switch with two ends of the current limiting reactor in parallel through a switch cabinet, the control over the high-capacity fast switch is realized at a secondary side, a control signal is activated by a triggering signal sent by an insulating transformer, and a control loop is powered by the power system of a 380V transformer substation. Limited by an insulation level, most high-capacity fast switches are used in a 6-35 kV high voltage chamber, and the high-capacity fast switches having many operational links, which are limited by many conditions, cannot be installed or used conveniently and are increased in the length of connecting bus bars, are more likely to malfunction and have more risks.
The short-circuit current of a power grid of 500 kV or below is usually limited at home and aboard using a power electronic technology which costs 10 times as much as domestic devices in construction and occupies a large floor area but cannot achieve a high operational reliability.
An ‘energy-saving current limiting device for a power grid’ was successfully developed in 2008 by Electric Power Research Institute of Ningxia, People's Republic of China, in cooperation with Kaili Group-Anhui Zhongxin Electric Power Technology Co., Ltd based on the concept of forming an integrated energy-saving current limiting device for a power grid by connecting a high-capacity fast switch with a current limiting reactor in parallel at a primary high-voltage side of a power grid put forward by Electric Power Research Institute of Ningxia in combination with the technical principle, structural parameters of product and technical parameters proposed by Electric Power Research Institute of Ningxia; as shown in FIG. 1 in which reference numeral 1 represents a control unit, reference numeral 2 represents an accumulator, reference numeral 3 represents a nonlinear resistor, reference numeral 4 represents a fuse, and reference numeral 5 represents a bridge, the bridge 5, the fuse 4 and the nonlinear resistor 3 of the current limiting device for a power grid are installed in a composite insulating sleeve, an inverted capacitor type voltage divider which also functions as an insulating support directly obtains the working power of a control system at the primary high-voltage side of the power grid so that the device is measured and controlled fully automatically and a plurality of parameters are intelligently determined fully automatically, thus, the application of the high-capacity fast switch is substantially improved; when used in a medium-voltage system (35 kV) of a 220 kV transformer substation in Ningxia, the energy-saving current limiting device for a power grid acts correctly in the case of a 35 kV short-line short-circuit fault, protecting a main transformer and other devices from being damaged by a too large short-circuit current and guaranteeing the safe and stable running of the system. However, after the high-capacity fast switch exploding bridge in the energy-saving current limiting device for a power grid is broken, power needs to be cut off for element replacement, thus causing a problem that the power grid is not high in operational reliability.
No effective solutions have been proposed to address the problem existing in the prior art that a power grid is not high in operational reliability.